As many as 60% of women with a pregnancy affected by gestational diabetes (GDM) will develop adult diabetes (Type 2 Diabetes Mellitus, or T2DM) in their next decade. Postpartum glucose testing and continued monitoring in primary care after delivery can identify women at risk, prevent or delay the onset of T2DM, and reduce the severity of complications associated with the disease. However, fewer than half of women with a GDM pregnancy get glucose tests, and very few transfer from obstetric care to primary care in the first six months after delivery. We will analyze data from a large insurance-based data system (OPTUMTM) in two steps. The first step is to identify barriers and facilitators to post-delivery glucose testing with the recommended 84 day period and transition to primary care for continued monitoring. In the second step, we will analyze the contribution of testing and transition to primary care to post-GDM health outcomes (repeat pregnancy with GDM, onset of T2DM, and increase in BMI (as a measure of increased risk for T2DM) within three years post- delivery. This 'big data' approach will provide the largest sample to date, and the first longitudinal analysis that begins prior to pregnancy and follows the same woman through for three years post-delivery. This data set has already been used to describe health care costs attributable to the economic burden of undiagnosed pre- diabetes, diabetes and gestational diabetes. Our proposed study will investigate both individual and systems factors that explain why the majority of women with GDM do not take advantage of post-delivery opportunities for prevention of T2DM.